Field of the Invention
The present invention relates to a variable nozzle mechanism used for a turbocharger.
Description of the Background Art
A turbocharger blows exhaust gas in a scroll path to a turbine wheel to rotatably drive the turbine wheel. Conventionally, in order to make a characteristic of the turbocharger variable, a variable nozzle mechanism is adopted in the turbocharger. The variable nozzle mechanism has a plurality of nozzle vanes moved to increase/decrease an area in cross section of a channel of exhaust gas to thus control a velocity of flow of exhaust gas blown to the turbine wheel.
Japanese Patent Laying-Open No. 2014-224498 proposes a variable nozzle mechanism in which an arm fit-engagement groove in which an arm of a variable nozzle engages is formed in a unison ring and the arm fit-engagement groove has a closing-side groove wall surface formed in a concave, arcuate shape and an opening-side groove wall surface formed in a convex, arcuate shape.
Japanese Patent Laying-Open No. 2014-224498 discloses that, of a wall surface of the arm fit-engagement groove, the closing-side groove wall surface normally contacting the arm as exhaust reaction force acts is formed in the concave, arcuate shape to reduce contact stress between the closing-side groove wall surface and the arm and hence wear on the arm and the closing-side groove wall surface. However, in order to suppress delayed supercharging or poor exhaust due to a nozzle vane's impaired positional precision, there is a demand for a variable nozzle mechanism for further reduction of wear on the arm and the unison ring, and conventional variable nozzle mechanisms are not necessarily sufficient and have room for improvement.